Video signal recording/reproducing apparatus

ABSTRACT

A reproducing apparatus adapted to a video signal recording/reproducing apparatus for reproducing a video signal recorded on a record medium in the form of an L-channel/S-segment recording system. The record medium travelling speed in production, the output from comparators and the guard band width are adjusted so that writing of the video signal in a field memory is effected so as not to cause omission of any portion of the video signal. Four embodiments are disclosed.

This application is a continuation of application Ser. No. 07/545,127,filed Jun. 26, 1990 which in turn was a continuation of application Ser.No. 07/114,651, filed on Oct. 28, 1987, both now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to video signal recording/reproducingapparatus wherein visually satisfactory images can be obtained withoutgenerating noise bands and reducing the signal-to-noise ratio in case ofa high or changed speed reproduction mode, such as the search mode.

2. Description of the Prior Art

Enhancement in quality of a picture based on changed or high speedreproduction of the VTR taking a recording system(one-channel/one-segment recording system) for recording video signalsfor one field on one track of a magnetic tape has heretofore beenattained by highly accurate control of the travelling of the magnetictape or by use of special reproduction heads. With recent tendencies toa decrease in price of semiconductor products such as memories and tohigher speed/higher density thereof, some VTRs have been offeredincorporating a field memory to execute changed speed reproduction. Thechanged speed reproduction making use of the field memory will beexplained as follows.

FIG. 1 is a schematic diagram illustrating a conventional changed speedreproduction system of a VTR which employs the field memory. Informationwhich has been recorded on a magnetic tape 1 is reproduced by means ofrotary heads 1a and 1b having different azimuth angles to each other.Outputs of the rotary heads 1a and 1b are transmitted to and amplifiedby head amplifiers 2a and 2b. Any one of the outputs of the headamplifiers 2a and 2b is selected by a switching circuit 3. The outputselected by the switching circuit 3 is given to a video signalprocessing circuit 4 which FM-demodulates the output from switchingcircuit 3. Then a video signal is reproduced and at the same time asynchronization signal is detected.

The output selected by the switching circuit 3 is also transmitted to anenvelope detecting circuit 5, thereby obtaining an envelope of thereproduced FM signal. The outputs of the envelope detecting circuit 5are supplied to a comparator 6 to be compared with a predeterminedlevel. A resulting signal from the comparator 6 is sent to a memorycontrol circuit 7. Then, the memory control circuit 7 supplies awrite-enable signal to a field memory 8 to carry out write-control onthe basis of the synchronization signal emitted from the video signalprocessing circuit 4 and of the control signal from the comparator 6,and further performs readout-control in asynchronism with thesynchronization signal.

A control head 9 is provided and serves to read a second control signalrecorded on the magnetic tape 1 in order to transmit it to a travellingcontrol circuit 10. The travelling control circuit 10 sends a drivesignal to a motor driver 11 on the basis of the second control signalread by the control head 9. Motor driver 11 drives a capstan motor 12.The rotation frequency of this capstan motor 12 is detected and sent tothe travelling control circuit 10.

Next, the operation of the reproduction system of the prior art VTR willbe described with reference to FIGS. 1 to 3 and in case of the highspeed reproduction which is effected at an N-fold speed [N=±2, ±4, ±6, .. . ; (±) indicates the travelling direction, (+) indicates thatreproduction is made in the same direction as that in the ordinaryreproduction, and (-) shows that the direction of reproduction isopposite to the ordinary direction]. FIG. 2(a) shows the relationbetween the recording tracks and the scanning loci of the heads when Nequals six and the magnetic tape runs in the direction indicated by thearrow X.

In FIGS. 2(a) and 2(b), "R" and "L" written on the tracks indicate thatthe portions marked with "R" and "L" have been recorded by the rotaryheads Ia and 1b or by other heads having the same azimuth angle asrotary heads 1a and 1b. The signals recorded on the portions depictedwith oblique lines are reproduced by the respective heads owing to theazimuth effect. The comparator 6 compares the outputs from the envelopedetecting circuit 5 with the predetermined level and then outputs asignal to the memory control circuit 7 when the former exceeds thelatter. Thus the memory control circuit 7 operates to write the outputsof the video signal processing circuit 4 to the field memory 8 when theoutput of the envelope detecting circuit 5 exceeds the predeterminedlevel. It follows therefore that in the field memory 8 the video signalscorresponding to one field are recorded in a pattern such as illustratedin FIG. 2(b).

On the other hand, the high definition television system which has beendeveloped as a television system for the next generation is now beingput into practical use. Such a high definition television system has awide video signal band of approximately 20 MHz. As a means for recordingsuch a wide band signal, the multichannel/multisegment recording systemhas been employed. Namely, the formation into multichannels contributesto reduction in the signal band width of one channel, while theformation into multisegments contributes to a rise in the speed of themagnetic tape relative to that of the rotary head, with the result thatthe recorded wavelength is increased. With this arrangement, the wideband signals are recorded and reproduced by the conventional magneticrecording technology.

An example wherein the two-channel/three-segment recording system isemployed will be explained hereinafter.

FIGS. 3(a) to 3(d) show the concept of the two-channel/three-segmentrecording system. In FIG. 3(a) illustrating the disposition of therotary heads, the numeral 13 denotes a rotary drum; 14a and 14brepresent rotary heads for recording/reproducing the signals of channelA (hereinafter referred to as CH. A); 15a and 15b designate the rotaryheads for recording/reproducing the signals of channel B (hereinafterreferred to as CH. B), the rotary heads 14a, 15a and 14b, 15b beingadjacently disposed. During recording, the rotary heads simultaneouslyperform the recording operation on both the channels A and B, asillustrated in FIG. 3(d). The magnetic tape is wound over the range of180° or more on the rotary drum 13 in recording and reproducing. Therotary drum 13 makes one and a half revolutions in the directionindicated by an arrowhead A in FIG. 3a during the one-field period,whereby the video signals of CHs. A and B for one field are recorded inthe form of the split three segments.

As shown in FIG. 3(c), an input video signal such as the compositesignal of one channel is allocated sequentially from above to theindividual segments of the respective channels by employing the fieldmemory on the basis of the unit of one horizontal scanning period.Therefore, a picture is, as illustrated in FIG. 3(b), divided into thetotal of six pictures, and each of the pictures thus obtained isrecorded on one track of the magnetic tape.

The reference symbols A1, A2, . . . recorded on the tracks shown in FIG.3(d) designate pieces of image information of the first, the second, . .. segments . . . of CH. A.

It is to be noted that it is possible to attain in a relatively easymanner high speed reproduction in a VTR which adopts themultichannel/multisegment recording system where the recording iseffected according to the above described tape format. To be specific,the lower part of the track corresponds to the upper part of thepicture, the central part corresponds to the central part of thepicture, and the upper part of the track corresponds to the lower partof the picture. For this reason, even if the order in which the sixpictures shown in FIG. 3(b) are superimposed on each other is slightlychanged, no visual problem arises because in the high speed reproductionthe motion of images appears to be unnatural. Namely, where the fetchinto the field memory is performed, when reproducing, for instance, theinformation A1, the reproduced outputs may not be input to the exactaddress into which the information A1 should be written. Instead, theimage information obtained by reproducing, for example, the informationA3, is input with respect to the address with which the information A1should be input. This does not cause serious visual problems.

In the changed speed reproduction from the VTR which takes themultichannel/multisegment recording system having the above-describedrecording format, if the full video information on the track iscompletely reproduced in a cycle within a given period, it is possibleto actualize satisfactory reproduction with no noise in the changedspeed reproduction, even if there is some unnaturalness.

FIG. 4 is a block diagram of a prior art video signalrecording/reproducing apparatus which adopts thetwo-channel/three-segment recording system. In the figure, the samereference numerals as used in FIG. 1 denote like elements. Referencenumerals 16a and 16b designate rotary heads for the CHs. A and B;reference numerals 17a and 17b designate rotary heads for the CHs; and4a and 4b stand for video signal processing circuits which produce avideo signal by effecting FM-demodulation and detect a synchronoussignal for A/D conversion. The reference numerals 7a and 7b stand formemory control circuits for executing write-control in response to thesynchronization signal emitted from the video signal processing circuit4a and 4b and for executing read-control in asynchronism with thesynchronization signal.

Field memory 8 comprises two memories 8a and 8b for CHs. A and B,respectively. The reference numeral 18 stands for a selector.

Next, the operation of the apparatus of FIG. 4 will be explained. Wherethe high speed reproduction is carried out at a speed N times therecording speed (N=±2, ±3, . . . : (±) indicates the travellingdirection. (+) shows the same direction as that of the ordinaryreproduction, and (-) shows the opposite direction), and when N=4, therelation between recording tracks and the head scanning loci isestablished as illustrated in FIG. 5(a). If the rotary heads for CHs. Aand B have different azimuth angles, the signals which are to bereproduced by the respective heads by virtue of azimuth effect comprisethose obtained from the portions depicted with the oblique lines on thetracks. Turning our attention to FIG. 5(b), reproduction envelopes to beemitted are shown. In the figure, no reproduction output is obtained inthe portions indicated by the oblique lines. As explained earlier, thevideo signal is recorded in such a tape format that the lower part ofthe track corresponds to the upper part of the picture, the central partcorresponds to the central part of the picture, and the upper partcorresponds to the lower part. Hence, the video information in the fieldmemory cannot be rewritten with respect to the portions depicted withthe oblique lines in FIG. 5(b). As a result, the fixed noise bands n, orthe noise bars shown in FIG. 5(c) are produced on the picture p.

Once such fixed noise bands n appear, the problem of being unable toobtain visually favourable images arises.

An example of a two-channel/three-segment recording system is givenbelow. The input image signals (composite signals of one channel) areallocated to two channels (CH. A and Ch. B) on the basis of a unit ofone horizontal scanning period (hereinafter referred to as 1H) and thelength of the time axis is doubled. As a result, the signal band widthof each channel is reduced to half the original width.

FIG. 6(a) shows the placement of the rotary heads. In FIG. 6(a), arotary drum 13 is provided with rotary heads 14a, and 14b forrecording/reproducing the signals of CH. A and rotary heads 15a and 15bfor recording/reproducing the signals of CH. B. The two pairs of rotaryheads 14a15a and 15b are contiguously disposed. The magnetic tape iswound at an angle of 180° on the rotary drum 13 at therecording/reproducing time. The rotary drum 13 makes one and a halfrevolutions during one field period. Hence, it follows that the imagesignals for one field are recorded so that the signals of CHs. A and Bare respectively split into three sections (three segments).

FIG. 6(b) shows a concept of the two-channel/three-segment recordingsystem. FIG. 6(c) illustrates a recording track pattern formed on themagnetic tape. A1, A2 and A3 shown on the tracks in FIGS. 6(b) and 6(c)indicate the image signals of the first, second and third segments whichare recorded by mans of the rotary heads 14a and 14b corresponding tochannel A.

The high speed reproduction in which the tape traveling velocity is, asin the prior art, set to be an integer multiple is now considered. WhenN=2, the relation between the recording tracks and the scanning loci ofthe heads is as shown FIG. 6(d). Where the rotary heads 14a, 14b, 15aand 15b have the same azimuth, no azimuth effect is present. Hence, itis possible to reproduce the image signals of all the tracks that theheads have traversed. While, on the other hand, as can be seen in thepotions depicted with the oblique lines in FIG. 6(e), there are sectionsin which the signals recorded by the rotary heads 14a and 14b and thesignals recorded by the rotary heads 15a and 15b are simultaneouslyread. The image signals are superposed on each other in these sections,whereby favorable outputs cannot be obtained.

Considering such circumstances, the output envelopes of the firstsegment CH. A are shown in FIG. 6(f). In the figure, the superpositiontakes place in the portions indicated by the oblique lines, and hence nogood picture is obtained.

FIG. 6(g) illustrates and actual picture. The portions shown by theoblique lines present a situation where the image information of thefield memory is not rewritten, and fixed noise bands are created suchthat a visually good picture is not acquired.

SUMMARY OF THE INVENTION

The conventional video signal recording/reproducing apparatus having theabove-described constitution is attended by problem of the existence ofthe drop out of the video signals at the time of the changed speedreproduction in spite of employing the field memory, which makes itimpossible to obtain visually favourable images.

Accordingly, it is a general object of the present invention to obviatethe above-stated problem.

It is another object of the present invention to provide a video signalrecording/reproducing apparatus capable of attaining high or changedspeed reproduction which brings about no decrease in the signal-to-noiseratio and creates no fixed noise band.

In order to achieve the above-stated objects, the first embodiment of avideo signal recording/reproducing apparatus in accordance with thepresent invention, take the form of a multichannel/multisegmentrecording system and is so constructed that a tape travelling speed athigh speed reproduction is set to be (N+m/M) times as high as that inrecording, wherein N=0, ±1, ±2, . . . , and m and M are positiveintegers but have no common divisor except one.

In this embodiment, by selecting the tape travelling speed properly inchanged speed reproduction, it is possible to obtain visuallysatisfactory pictures with no sharp drop in the signal-to-noise ratioand no fixed noise band.

The second embodiment of a video signal recording/ reproducing apparatusin accordance with the present invention takes the L-channel/S-segmentrecording system and reproduces information from a record medium bymoving the medium at travelling speed (N+1/L) times as high as that inrecording, wherein N=0, ±1, ±2, . . .

The third embodiment of a video signal recording/reproducing apparatusaccording to the present invention takes the form of theone-channel/multisegment recording system and reproduces informationfrom a record medium by moving the medium at a travelling speed aneven-number of times as high as that in recording when the guard band isrelatively narrow and at a travelling speed (N+1/2) times as high asthat in recording when the guard band is relatively wide, wherein N=0,±1, ±2, . . .

In order to achieve the above-stated objects, the fourth embodiment of avideo signal recording/reproducing apparatus according to the presentinvention is arranged so that special reproduction heads are jointlyused at the time of high speed reproduction, and that the specialreproduction heads are disposed to scan positions deviating by a (n+1/2)track pitch, b being an integer, from the tracks scanned by ordinaryreproduction. When high speed reproduction is effected, the specialreproduction heads and the ordinary heads are changed over at a constantperiod, thereby obtaining reproduced images without any sharp decreasein the signal-to-noise ratio and no fixed noise band.

The above and other objects and advantages of the invention will becomeapparent more fully hereinafter from a consideration of the followingdescription presented in connection with the accompanying drawingswherein some embodiments are illustrated by way of examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a video signal recording/reproducingapparatus which adopts a conventional one-channel/one-segment recordingsystem;

FIGS. 2(a) and 2(b) illustrate the operation of the apparatus shown inFIG. 1;

FIGS. 3(a) to 3(d) show the concept of the two-channel/three-segmentrecording system;

FIG. 4 is a block diagram of another conventional video signalrecording/reproducing apparatus which adopts themultichannel/multisegment recording system;

FIGS. 5(a) to 5(c) illustrate one mode of operation of the apparatusshown in FIG. 4 when the two-channel/three-segment recording system isemployed:

FIGS. 6(a) to 6(g) illustrate another mode of operation of the apparatusshown in FIG. 4;

FIG. 7 is a block diagram of the first embodiment of a video signalrecording/reproducing apparatus according to the present invention;

FIG. 8(a) to 8(e) illustrate an operation of the apparatus shown in FIG.7;

FIG. 9 is a block diagram of the second embodiment of a video signalrecording/reproducing apparatus according to the present invention;

FIGS. 10(a) to 10(d) illustrate one mode of operation of the apparatusshown in FIG. 9;

FIGS. 11(a) to 11(c) illustrate one mode of operation of the thirdembodiment of a video signal recording/reproducing apparatus accordingto the present invention;

FIGS. 12(a) to 12(c) illustrate another mode of operation of the thirdembodiment;

FIG. 13 is a block diagram of the fourth embodiment of a video signalrecording/reproducing apparatus according to the present invention;

FIG. 14(a) shows the disposition of the heads used in the apparatusshown in FIG. 13;

FIG. 14(b) and 14(c) shows how the heads are placed on the tracks in theapparatus shown in FIG. 13;

FIGS. 15(a) to 15(e) illustrate one mode of operation of the apparatusshown in FIG. 13;

FIGS. 16(a) to 16(c) illustrate another mode of operation of theapparatus shown in FIG. 13; and

FIGS. 17(a) and 17(b) show another example of the disposition of theheads used in the apparatus shown in FIG. 13

In these figures, like elements or parts are designated by the samereference numerals or symbols.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 7 shows the first embodiment of a video signalrecording/reproducing apparatus according to the present invention. Inthis figure, the same reference symbols are embodiment, the amplifiedvideo signals from video amplifier 2a are fed to an envelope detectingcircuit 5a where the envelopes are detected.

The outputs of the envelope detecting circuit 5a are sent to acomparator 6a which compares the envelope of the signals with apredetermined signal level. The resulting comparison signal is emittedand given to a memory control circuit 7a. The memory control circuit 7aperforms write-circuit control to field memory 8 on the basis of thesynchronization signals emitted from the video signal processing circuit4a and the outputs of the comparator 6a, and further performsread-control in asynchronism with the synchronization signals.

An envelope detecting circuit 5b, a comparator 6b and a memory controlcircuit 7b are constructed in the same manner as the envelope detectingcircuit 5a, the comparator 6a and the memory control circuit 7a.

The operation of the first embodiment shown in FIG. 7 will be explainedby taking one example in which the two-channel/three-segment recordingsystem is adopted and the tape travelling speed is so set as to be(3+1/4) times as high as that in recording.

FIG. 8(a) shows the relation between the recording tracks and the headscanning loci. Assuming that the heads for CHs. A and B have the sameazimuth angle, no azimuth effect appears, and the video signals of allthe tracks that the heads have traversed can be reproduced. Directingattention to the reproduced output of CH. A, the reproduced outputenvelopes are obtained as illustrated in FIG. 8(b). While on the otherhand, as can be seen in the portions indicated by the oblique lines inthe figure, there exist some sections in which a portion of informationrecorded by the heads 16a and 16b and a portion of information recordedby the heads 17a and 17b are simultaneously read. The satisfactoryreproduced video outputs cannot be obtained in these sections.

In order to avoid such a superimposition, the adjustment of the guardband width and the outputs of the comparators 6a and 6b is adequatelymade.

Turning attention now to the outputs of CH. A during the period of twoscannings, the output envelopes of the adjacent two periods of onescanning are positioned to interpolate each other. The good outputswithout any drop out in the video signal are, as illustrated in FIG.8(c), gained when forming the video information for one track by makinguse of the output envelopes during the period of two scannings.

The reading process from the field memory 8 is effected in asynchronismwith the writing process. As shown in FIG. 8(c), the output level of thereproduced video signals stored in the field memory 8 is relativelylarge, and the signal-to-noise ratio of the video signals to be read outis not so deteriorated that the pictures are difficult to distinguish.Since all the data stored in the field memory 8 are rewritten during theperiod of two fields, it is possible to actualize the desirable highspeed reproduction without any fixed noise band.

When only one channel is used, it follows that the contents of the fieldmemory are rewritten in the cycle of four fields.

Turning attention now to the output from, for instance, CH. A, FIG. 8(d)illustrates envelopes of CH. A for the period of four fields on thebasis of the relation, as shown in FIG. 8(a), between the track patternsand the scanning loci of the heads. The portions drawn by the obliquelines indicate the output envelopes of the first segment A1 of CH. A.Reformation of these envelopes leads to the image signals shown in FIG.8(e). It can be understood from FIG. 8(e) that a similar performance canbe obtained simply by using one channel. As a result of this, it ispossible to provide the effect of simplifying the processing of thesignals written in the field memory 8.

It is to be noted that the same effects can be obtained by properlyselecting the tape travelling speed to be (N+m/M) times as high as thatin recording when using the multichannel/multisegment recording system.It is also to be noted that an effect similar to that in the case of theheads having the same azimuth angle are exhibited in such a case whereeach head has an azimuth angle which differs in every channel.

In these cases, the following conditions should be met:

N=0, ±1, ±2, ±3, . . . ;

M=2, 3, 4, . . . ;

m=1, 2, 3, . . . ;

M>m; and

M and m have no common divisor except one.

The tape travelling speed should be determined so that there exists nointeger r which satisfies the following equation:

    (N+m/M)×M×k=r×s

S: the number of the segments, equal to or greater than two

N: integer

M: 2, 3, 4, . . .

m: 1, 2, 3, . . . M>m

k: 1, 2, 3, . . . S-1.

If the respective channels have the same azimuth angle, the followingcondition in addition to the above-described conditions must besatisfied. Let the number of the channels be L, an integer M should bedetermined so that M is not equal to L. Moreover. M should be determinedso that M and L have no common divisor except one when M is smaller thanL.

The following is the reason why such a restriction is imposed on thedetermination of the tape travelling speed. In the VTR which adopts theS-segment recording system, the contents in the field memory arerewritten in the cycle of M fields in reproduction at a speed (N+m/M)times as high as that in ordinary reproduction. If the above-mentionedconditions are met [namely, if there exists a natural number rsatisfying the equation (N+M/m)×M×k×r×S], the rewritten cycle comes tokM/S, M being larger than kM/S, and a return to the initial state ismade before all the contents of the image signals are rewritten.Consequently, the fixed noise bands are produced, and any goodreproduced pictures can not be acquired in the changed speedreproduction. If all the heads have the same azimuth angle, the videosignals are superimposed on each other, as stated before, and the outputenvelopes are obtained as shown in FIG. 8(b). When determining M so thatL is equal to M, the position in which the favourable envelope isemitted retains unchanged for every sequential scanning period, wherebydrop out occurs in the video signals depicted with the oblique lines. Asa result, the fixed noise bands appear, and hence any satisfactoryreproduced pictures cannot be obtained in the changed speedreproduction.

In the first embodiment, one example has been explained in which thereproduction speed is (3+1/4) times the recording speed and thetwo-channel/three-segment recording system is adopted. Although thedemonstration is omitted, in the high speed reproduction having theheads of the same azimuth angle and taking themultichannel/multisegment, multichannel/one-segment, andone-channel/multisegment recording system, if the tape travelling speedsatisfies the aforementioned condition, and when the following formulais established,

    M=2×L

wherein L is the number of channels, the high speed reproduction can becarried out and brings about similar effects.

Referring now to FIG. 9, the second embodiment of a video signalrecording/reproducing apparatus according to the present invention isshown. In this figure, like elements are designated by the samereference numerals and symbols as used in FIGS. 4 and 7, and thedescription is therefore omitted herein.

Now, the operation of the apparatus will be explained by taking oneexample in which the tape travelling speed is so set as to be (3+1/2)times as high as that in recording and the two-channel/three-segmentrecording system is adopted. In this example, a pair of heads 16a and16b and a pair of heads 17a and 17b have different azimuth angles,respectively.

FIG. 10(a) shows the relation between the recording tracks and the headscanning loci. Since CHs. A and B have the different azimuth, theenvelopes as shown in FIG. 10(b) are emitted by virtue of the azimutheffect. In this case, the output envelopes for two adjacent periods ofone scanning are positioned to interpolate each other. At this time, theoutput level of the comparators 6a and 6b as well as the guard bandwidth is properly adjusted, thereby obtaining the output envelopes shownin FIG. 10(c). The satisfactory outputs without any drop in the videosignal are gained as illustrated in FIG. 10(d), when forming the videoinformation included in one track by using the output envelopes for theperiod of two scannings.

The reading operation from the field memory 8 is executed inasynchronism with the writing operation. As illustrated in FIG. 10(d),the output level of each reproduced video signal stored in the fieldmemory 8 is relatively high, and the signal-to-noise ratio of the videosignal to be read out is not deteriorated to the extent that the pictureis difficult to distinguish. All the data stored in the field memory 8are rewritten for the period of two fields, and the high speedreproduction without any fixed noise band can therefore be attained.

Here, explanation will be made about a video signalrecording/reproducing apparatus in the third embodiment which takes theone-channel/multisegment recording system. The construction of theapparatus is the same as that illustrated in the block diagram of FIG.9, and hence the description thereof is omitted. The two heads used inthis case have different azimuth angles.

The operation will be explained by taking one example in which the tapetravelling speed is four times that in recording.

As described already, the relation between the recording tracks and thescanning loci of the heads becomes the one illustrated in FIG. 11(a). Inthe figure, the signs R and L indicate the portions recorded by theheads each having a different azimuth angle. Since the heads of CHs. Aand B have different azimuth angles, only the portions depicted with theoblique lines are reproduced by virtue of the azimuth effect. The outputenvelopes for the period of two scannings which are shown in FIG. 11(b)are similar to those shown in FIG. 10(b). Also in this case, theadjacent output envelopes are positioned to interpolate each other. Atthis time, the video information for one track is formed by properlyadjusting the output level of the comparators 6a and 6b as well as theguard band width, thereby obtaining, good outputs without any drop outin the video signal, as shown in FIG. 11(c).

As the guard band width increases, the signal-to-noise ratio isextremely deteriorated in spite of the interpolation, because theoutputs from the portions between adjacent envelopes are considerablysmall.

In order to avoid such deterioration in the signal-to-noise ratio in thecase of a relatively large guard band width, the tape travelling speedis set to be (4+1/2) times as high as that in recording. In this case,the relation between the recording tracks and the scanning loci of theheads is shown in FIG. 12(a), which is similar to that shown in FIG.11(a). Since the heads of CHs. A and B have different azimuth angle, theportions shown by the oblique lines are therefore reproduced owing tothe azimuth effect. The output envelopes for the period of fourscannings are illustrated in FIG. 12(b). The output envelopes for thisperiod are likewise positioned to interpolate each other. The videoinformation for one track is formed by properly adjusting the outputs ofthe comparators 6a and 6b. As a result, the satisfactory outputs whoselevel is relatively large are obtained, as illustrated in FIG. 12(c),without omission of any video signal.

The readout from the field memory is effected in asynchronism with thewriting operation. When the guard band width is relatively small, thetape travelling speed is set so as to be four times as high as that inrecording, whereby the output level of the video signals stored in thefield memory is relatively large as shown in FIG. 11(c). In addition,the signal-to-noise ratio of the video signal to be read out is not sodeteriorated that the picture becomes difficult to distinguish.

When the guard band is relatively large, the tape travelling speed isset to be (4+1/2) times as high as that in recording. In consequence,the output level of the reproduced video signals stored in the fieldmemory is, as shown in FIG. 12(a), relatively large, and thesignal-to-noise ratio of the video signal to be read out is not sodeteriorated that the picture becomes difficult to distinguish.

All the data in the field memory are rewritten in the cycle of twofields at the reproducing speed four times or (4+1/2) times therecording speed, so the good high speed reproduction without fixed noiseband can be realized.

The explanations made in connection with the second and thirdembodiments lead to the following general conclusion: 1) where themultichannel/multisegment recording system (the number of the channelsis hereinbelow referred to L) is adopted and the head for each channelhas a different azimuth angle, the tape travelling speed should be setat (N+1/L) times (N: 0, ±1, ±2, ±3, ±4, . . . ) as high as that inrecording; and 2) where the one-channel/multisegment recording system isemployed and two heads have different azimuth angles, the tapetravelling speed should be set to be M times (M is an even number) ashigh as that in recording when the guard band is relatively narrow, andshould be set to be (N+1/2) times (N: 0, ±1, ±2, . . . ) as high as thatin recording when the guard band is relatively large.

Referring now to FIG. 13, the fourth embodiment of a video signalrecording/reproducing apparatus according to the present invention isshown in a block-diagramatic form. In this figure, like elements aredesignated by the same reference symbols as used in FIG. 7.

In FIG. 13, a pair of special reproduction heads 19a and 19b areprovided and connected to a first head change-over switch 21a, andanother pair of special reproduction heads 20a and 20b are provided andconnected to a second head change-over switch 21b. Ordinary heads 16a,16b and special reproduction heads 19a and 19b reproduce information onCH. A and ordinary heads 17a, 17b and special reproduction heads 20a and20b reproduce information on CH. B.

Head change-over switch 21a serves to change over the signals at aconstant period which are reproduced both by the ordinary heads 16a and16b and by the special reproduction heads 19a and 19b at the time ofspecial reproduction. Head change-over switch 21b similarly serves tochange over the signals at a constant period which are reproduced bothby the ordinary heads 17a and 17b and by the special reproduction heads20a and 20b at the time of special reproduction.

Outputs of the head change-over switch 21a are transmitted to headamplifier 2a, while the outputs of the head change-over switch 21b aresent to head amplifier 2b.

FIG. 14 is a diagram illustrating a disposition of the heads used in thefourth embodiment of the present invention, and FIG. 15 is a diagramillustrating the operation of this embodiment.

Now, the operation of the fourth embodiment of the present inventionwill hereinafter be described with reference to FIGS. 13 to 15. Each ofthe special reproduction heads 19a, 19b, 20a and 20bis, as illustratedin FIG. 14(a), disposed to scan the position deviating by a 1/2 trackpitch from the track to be scanned by the corresponding ordinary heads,as shown in FIG. 14(b). Consequently, in a case where the ordinary heads16a, 16b, 17a and 17b and the special reproduction heads 19a, 19b, 20aand 20b are changed over for every revolution of the rotary drum at thetime of high speed reproduction, the relation between the track patternsand the scanning loci of the heads is the one illustrated in FIG. 14(c).

Now, an assumption is made that the tape travelling speed is twice ashigh as that in recording, and that the two-channel/three-segmentrecording system is employed. The ordinary heads 16a, 16b, 17a and 17band the special reproduction heads 19a, 19b, 20a and 20b have the sameazimuth angle. FIG. 15(a) shows the relation between the recorded tracksand the scanning loci of the heads. The reference signs A1, A2 and A3designate the recorded tracks of CH. A, and B1, B2 and B3 designate therecorded tracks of CH. B. Every time the rotary drum makes one and ahalf revolutions (one field period), the special reproduction heads 19a,19b, changed over. Accordingly, the output envelope waveform as shown inFIG. 15(b) is obtained from the ordinary heads 16a, 16b, 17a and 17b,while the reproduction envelope waveform as shown in FIG. 15(c) isobtained by the special reproduction heads 19a, 19b, 20a and 20b. Sincethe ordinary heads and the special reproduction heads have the sameazimuth angle, no azimuth effect appears. Therefore, the portions of thereproduced signals from the adjacent tracks are superimposed to eachother, as depicted with oblique lines. The outputs of the comparators 6aand 6b and the guard band width should be properly adjusted in order toprevent such superimposition of the signals from occurring. The envelopeoutputs obtained by the ordinary heads and the special reproductionheads are in such a position that they interpolate each other.

The output envelopes reproduced during the period of two fields and thetrack positions are illustrated in FIG. 15(d) in the light of the factthat the relation between the scanning loci of the heads and the trackpatterns is repeated in the cycle of two fields. In FIG. 15(d), theportions depicted with the oblique lines indicate the reproduced outputsfrom the tracks A1. When making reformation, the reproduced outputswithout any drop out of the video signal can be obtained, as illustratedin FIG. 15(e).

The readout from the field memory 8 is executed in asynchronism with thewriting operation. As shown in FIG. 15(e), the output level of eachreproduced video signal stored in the field memory 8 is relativelylarge, and the signal-to-noise ratio of the video signals to be read isnot so deteriorated that the picture is difficult to distinguish. Allthe data are rewritten once for every two fields, and hence no fixednoise band is created. This makes it possible to attain extremelysatisfactory high speed reproduction.

In the fourth embodiment, the two pairs of special reproduction heads19a, 19b, 20a and 20b are employed. The same effects can, however, beacquired by merely using two special reproduction heads 19b and 20b.Such a modification will be explained with reference to FIG. 16.

FIG. 16(a) shows the relation between the track patterns and thescanning loci of the heads. The ordinary heads 16a, 16b, 17a and 17b andthe special reproduction heads 19b and 20b are changed over for everyhalf revolution of the rotary drum. The output envelopes reproducedduring the period of two fields and the track positions are illustratedin FIG. 16(b) in the light of the fact that the above-mentioned relationis repeated in the cycle of two fields. In FIG. 16(b), the portionsshown by the oblique lines indicate the reproduced outputs from thetracks A1. When making the reformation, the reproduced outputs withoutany drop out of the video signal can be produced, as can be seen in FIG.16(c). Hence, it is possible to exhibit the effects similar to thosedescribed in the embodiment of FIG. 13 only by employing two specialreproduction heads 19b and 20b.

The fourth embodiment has been explained as one example of the casewhere the two-channel/three-segment recording system is adopted and thereproduction is made at double the recording speed. It is, however,possible to provide the same effects even when information recorded inthe multichannel/multisegment system is reproduced at a speed more thandouble the ordinary reproduction speed and the special reproductionheads are disposed to scan the positions deviating by a track pitch of a(1/2+n) track pitch, n being an integer, from the track to be scanned bythe corresponding ordinary heads.

It should be noted that similar effects can also be acquired in a casewhere the multichannel/one-segment recording system or theone-channel/multisegment recording system is adopted.

In the above-described fourth embodiment, the heads are changed over forevery period of one field. It is, however, possible to obtain goodreproduced images without a noise band by switching the heads for everyone rotation or every one and a half rotations of the heads.

On this point, it is to be noted that when a tape travelling speed isdetermined to be M times the ordinary reproduction speed, M being aninteger, so that there is no integer r which satisfies the followingequation:

    M×k=r×S

wherein

S: the number of the segments, larger than two

k: 1, 2, 3, . . . , S-1.

This condition restrictive to the determination of the tape travellingspeed is attributed to the following reason. In the changed speedreproduction of the VTR which takes the S-segment recording system, thecontents stored in the field memory are in general rewritten in thecycle of two fields. When the above-described condition is satisfied,that is, when there exists such as integer r that satisfies the equationM×k=r×S, however, the rewrite cycle comes to 2k/S (2>2k/S), and a returnto the initial state is made before all the contents of video signals inthe field memory are rewritten. As a result of this, the fixed noisebands are produced, and any satisfactory images cannot be obtained inthe changed speed reproduction.

In the fourth embodiment, similar effects have been obtained by use oftwo special reproduction heads, one corresponding to CH. A and the othercorresponding to CH. B, in the case where the two-channel/three-segmentrecording system is employed. It is also possible in the case of themultichannel recording system, to obtain satisfactory reproduced imageswith no fixed noise band by providing the special reproduction heads thenumber of which is equal to that of the channels, viz., each of whichcorresponds to each of the channels.

In the description given above, the ordinary heads 16a, 16b, 17a and 17band the special reproduction heads 19a, 19b, 20a and 20b are disposed insuch a way as illustrated in FIG. 14(a). If the foregoing conditions aremet, similar effects can be obtained by the ordinary heads and specialreproduction heads placed in such manners as shown in FIG. 17(a) and17(b).

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A video signal recording and reproducingapparatus wherein a video signal of one field period, including asynchronization signal, is recorded on a plurality of tracks on arecording medium in an L-channel/S-segment recording system, L and Sbeing respectively positive integers which are never simultaneouslyequal to one, comprising:at least one rotating reproducing head providedfor each of the L-channels for reproducing a video signal on saidrecording medium; processor means coupled to said rotating reproductionhead for demodulating the video signal reproduced by said rotatingreproduction head and detecting the synchronization signal from thevideo signal, said processor means outputting the demodulated videosignal and said synchronization signal; storing means capable of storinga video signal of at least one field period for storing the video signaloutput from said processor means; storage control means for controllingsaid storing means so that the video signal is written in said storingmeans in synchronism with the detected synchronization signal when thelevel of the reproduced video signal exceeds a predetermined level andso that the video signal is read out in asynchronism with thesynchronization signal; and recording medium travel control means forselecting the traveling speed of said recording medium so that in thecase of high speed playback, said recording medium travel control meansselects the traveling speed of said recording medium to be (N+m/M) timesthe recording speed, N being equal to 0, ±1, ±2, . . . , and m and Mbeing positive integers having no common divisor except one and so thatno integer r exists which satisfies the equation (N+mM)×M×k=r×S, whereinS is the number of segments k=1, 2, 3, . . . S-1 and M>m.
 2. Anapparatus as claimed in claim 1 wherein said processor means includescomparator means coupled to said rotating reproduction head forcomparing the level of the reproduced video signal with a predeterminedlevel.
 3. An apparatus as claimed in claim 1, wherein M is not equal toL when all of said rotating reproduction heads have the same azimuthangle.
 4. A video signal recording and reproducing apparatus wherein avideo signal of one field period, including a synchronization signal, isrecorded on a plurality of tracks on a recording medium in anL-channel/S-segment recording system, L being an integer equal to atleast 2, and S being an integer equal to at least 1, comprising:at leastone rotating reproducing head provided for each of the L-channels forreproducing a video signal on said recording medium ,wherein azimuthangles of said rotating reproducing heads are different for eachchannel; processor means coupled to said rotating reproduction head fordemodulating the video signal reproduced by said rotating reproductionhead and detecting the synchronization signal from the video signal,said processor means outputting the demodulated video signal and saidsynchronization signal; storing means capable of storing a video signalof at least one field period for storing the video signal output fromsaid processor means; storage control means for controlling said storingmeans so that the video signal is written in said storing means insynchronism with the detected synchronization signal when the level ofthe reproduced video signal exceeds a predetermined level, and so thatthe video signal is read out in asynchronism with the synchronizationsignal, and recording medium travel control means for selecting atraveling speed for said recording medium so that when high speedplayback occurs, said recording medium travel control means selects thetraveling speed for said recording medium to be (N+1/L) times therecording speed, N being equal to 0, ±1, ±2, . . .
 5. A video signalrecording and reproducing apparatus wherein a video signal of one fieldperiod, including a synchronization signal, is recorded on a pluralityof tracks on a recording medium in a single-channel/S-segment recordingsystem, S being a positive integer unequal to 1, and wherein guard bandsare provided between the tracks on the recording medium comprising:atleast one pair of rotating heads for producing the video signal on saidrecording medium; processor means coupled to said rotating reproductionheads for demodulating the video signal reproduced by said rotatingreproduction heads, and detecting the synchronization signal from thevideo signal, said processor means outputting the demodulated videosignal and said synchronization signal; storing mans capable of storinga video signal of at least one field period for storing the video signaloutput from said processor means; storage control means or controllingsaid storing means so that said video signal is written in said storingmeans in synchronism with the detected synchronization signal when thelevel of the reproduced signal exceeds a predetermined level, and sothat the video signal is read out in asynchronism with thesynchronization signal, and recording medium travel control means forselecting a traveling speed for said recording medium so that when achange in reproduction speed occurs, said recording medium travelcontrol means selects the traveling speed of said recording medium to beM times the recording speed, M being an even integer when said guardbands have a width less than a predetermined width, and to be (N+1/2) ashigh as the recording speed, N being equal to 0, ±1, ±2, . . . when saidguard bands have a width greater than said predetermined width.
 6. Avideo signal recording and reproducing apparatus wherein a video signalof one field period, including a synchronization signal, is recorded ona plurality of tracks on a recording medium comprisingL-channel/S-segment recording system, L and S being respectivelypositive integers which are not simultaneously equal to 1, comprising:atleast one rotating reproducing head provided for each of the L-channelsfor reproducing a video signal on said recording medium, all of saidrotating reproduction heads having equal azimuth angles; processor meanscoupled to said rotating reproduction head for demodulating the videosignal reproduced by said rotating reproduction head and detecting thesynchronization signal from the video signal, said processor meansoutputting the demodulated video signal; storing means capable ofstoring a video signal of at least one field period for storing thevideo signal output from said processor means; storage control means forcontrolling said storing means so that the video signal is written insaid storing means in synchronism with the detected synchronizationsignal when the level of the reproduced signal exceeds a predeterminedlevel, and so that the video signal is read out in asynchronism with thesynchronization signal, and recording medium travel control means forselecting a traveling speed for said recording medium so that when highspeed playback occurs, said recording medium travel control meansselects a traveling speed of the recording medium to be (N+1/2L) timesthe recording speed, N being equal to 0, ±1, ±2, . . .
 7. A video signalrecording and reproducing apparatus wherein the video signal of onefield period is recorded on a plurality of tracks on a recording mediumin an L-channel/S-segment recording system, L and S being respectivelypositive integers which are not simultaneously equal to 1, and whereinsignals reproduced from reproduction heads are stored in a field memory,comprising;ordinary reproduction rotating heads for recordinginformation on said recording medium, special reproduction rotatingheads provided to be used when a change in reproduction speed occurs,the number of said special reproduction rotating heads being equal tothe number of said ordinary reproduction rotating heads, said specialreproduction heads being arranged to scan positions (n+1/2) times thetrack pitch apart from the tracks scanned by said ordinary reproductionrotating heads when ordinary reproduction is performed on correspondingchannels, n being an integer, switch means for switching a reproducedsignal from said ordinary reproduction heads and a reproduced signalfrom said special reproduction heads, during changed speed reproduction,at a switching period equal to one-half of the rotation interval of saidrotating heads multiplied by an integer; and field memory controllingmeans for causing, when a level of either of the switched reproducedsignals exceeds a predetermined level after the switching of thereproduced signals by said switch means, the reproduced signal whichexceeds the predetermined level to be written in said field memory insynchronism with a synchronization signal obtained from the reproducedsignal, and causing signals stored in said field memory to be read outin synchronism with said synchronization signal.
 8. A video signalrecording and reproducing apparatus wherein a video signal of one fieldperiod is recorded on a plurality of tracks on a recording medium in anL-channel/S-segment recording system, L and S being respectivelypositive integers which are not simultaneously equal to 1, and whereinsignals reproduced from the reproduction heads are stored in a fieldmemory, comprising:ordinary reproduction rotating heads for recordinginformation on said recording medium, special reproduction rotatingheads provided to be used when a change in reproduction speed occurs,the number of said special reproduction rotating heads being equal tothe number of said ordinary reproduction rotating heads being arrangedto scan positions (n+1/2) times the track pitch apart from the tracksscanned by said ordinary reproduction rotating heads when ordinaryreproduction is performed on the corresponding channels, n being aninteger, and switch means for switching a reproduced signal from saidordinary reproduction heads and a reproduced signal from said specialreproduction heads, during changed speed reproduction, at a switchingperiod equal to one-half of the rotation interval of said rotating headsmultiplied by an integer; and field memory controlling means forcausing, when a level of either of the switched reproduced signalsexceeds a predetermined level after the switching of the reproducedsignals by said switch means, the reproduced signal which exceeds thepredetermined level to be written in said field memory in synchronismwith a synchronization signal obtained from the reproduced signal, andcausing signals stored in said field memory to be read out insynchronism with said synchronization signal.
 9. A video signalrecording and reproducing apparatus wherein a video signal of one fieldperiod, including a synchronization signal, is recorded on a pluralityof tracks on a recording medium in an L-channel/1-segment recordingsystem, L being a positive integer larger than one, comprising:at leastone rotating head provided for each of the L-channels for reproducing avideo signal on said recording medium; processor means coupled to saidrotating reproduction head for demodulating the video signal reproducedby said rotating reproduction head and detecting the synchronizationsignal in the video signal, said processor means outputting thedemodulated video signal and synchronization signal; storing meanscapable of storing a video signal of at least one field period forstoring the video signal output from said processor means; storagecontrol means for controlling said storing means so that the videosignal is written in said storing means in synchronism with the detectedsynchronization signal when the level of the reproduced video signalexceeds a predetermined level and so that the video signal is read outin asynchronism with the synchronization signal; and recording mediumtravel control means for selecting the traveling speed of said recordingmedium so that in the case of a high speed playback, said recordingmedium travel control means selects the traveling speed of saidrecording medium to be (N+m/M) times the recording speed, N being equalto 0, ±1, ±2, . . . , and m and M being positive integers having nocommon divisor except one.